A sheath valve is a type of "one-way" valve which permits a liquid, gas, or other flowable material to be dispensed preferentially in one direction, but does not permit backflow through the valve during or upon cessation of dispensing, and so prevents possible contamination to the contents remaining in the dispensing container.
One form of one-way valve is a cylindrical core encompassed by an elastic cylindrical sheath, with the core having an entrance tube therein leading to a portion of the sheath, and an exit tube leading from the sheath. The two tubes are closed by the sheath and do not interconnect; but pressure applied to the liquid being dispensed serves to expand the sheath so that the liquid can pass from the entrance tube to the exit tube. Upon release of the pressure, the sheath contracts, sealing the valve against any possible reverse contamination.
Various patents have issued directed to this cylindrical valve. Examples of these include Gerber U.S. Pat. No. 4,846,810; Debush Pat. Nos. 5,279,330; 5,305,783; and 5,305,786; and Pardes U.S. Pat. No. 5,092,855. Each of these uses a cylindrical sheath surrounding a cylindrical valve core. This cylindrical structure is not only difficult and costly to manufacture, but also difficult and costly to assemble. A problem with a cylindrical sheath valve is that, to maintain tension, the inside diameter of the cylindrical sheath should be smaller in diameter than the outside diameter of the core, resulting in difficult assembly.
This present invention is directed to a sheath structure using a planar elastomeric membrane which is simpler and cheaper to manufacture, but provides an effective preferential flow valve that prohibits non-coerced backflow contamination.